1. Field of the Invention
The present invention generally relates to projecting a two-dimensional image of high quality and brightness, especially in color.
2. Description of the Related Art
It is generally known to project a two-dimensional image on a projection surface based on a pair of scan mirrors which oscillate in mutually orthogonal directions to scan a laser beam over a raster pattern comprised of a plurality of scan lines. One of the scan mirrors, sometimes referred to herein as an X-mirror, sweeps the laser beam at a relatively faster speed generally along a scan direction extending along the horizontal, and the other of the scan mirrors, sometimes referred to herein as a Y-mirror, sweeps the scan line at a relatively slower speed generally perpendicular to the scan direction extending along the vertical. The X-mirror is oscillated, typically at resonance, at a scan frequency.
The image is created in the raster pattern by energizing or pulsing a laser on and off at selected times. A host supplies an incoming video signal having vertical and horizontal synchronization data, as well as video and clock data, at a data frequency to a buffer for storage and, in turn, to the laser to be pulsed under the command of a microprocessor.
Although generally satisfactory for their intended purpose, a frequency mismatch often occurs in known image projection systems between the data frequency of the video signal and the scan frequency of the X-mirror. This mismatch causes problems. For example, if the X-mirror is scanning at a lower frequency than the data frequency of the video signal, then the buffer requires a substantial amount of memory to accommodate the incoming video signal. If the X-mirror is scanning at a higher frequency than the data frequency of the video signal, then the host cannot deliver the data fast enough to draw the image. The brightness of the image, as well as a lack of brightness uniformity, is also affected by variations in the scan frequency.